Generally, a transmission capable of being used in a two-wheeled vehicle such as an electric power assisted bicycle and an electric scooter, or a multi-wheeled vehicle, and performing a change of speed using two motors has been known.
In such a transmission, a planetary gear unit is disposed. When a rotational torque is applied to one of two input shafts (a sun gear and a ring gear) according to an operation of one of the two motors, a torque which rotates an input shaft of the other motor in a reverse direction is generated. At this time, in order for the input shaft of the other motor not to be rotated, a current applied to the other motor so as to generate a stop torque, or an electromagnetic brake system which fixes or releases a gear connected to the other motor is installed to forcibly fix the gear.
However, when the current is applied to the other motor so as to generate the stop torque, power consumption occurs, and the other motor generates heat while the stop torque is generated. Further, when the electromagnetic brake system is installed, there are some problems that an entire volume of the transmission is increased, and a time delay caused by a mechanical operation occurs. Furthermore, there is another problem that the electromagnetic brake system consumes a predetermined amount of electric power.